FFT of a signal (non constant time)

In summary, the speaker took the FFT of a signal with a non-constant time period, but a sampling frequency of 6.5Hz. They questioned if this was possible and meaningful. The speaker also mentioned using Matlab's FFT command, which uses the Cooley-Tukey FFT algorithm. They clarified that over all, there were 719 data points taken at a non-constant time period for a total time period of 111.8 seconds. However, the signal is clearly periodic and the speaker wanted to see the frequencies using the FFT. They were unsure if this was a valid approach and suggested using interpolation to achieve a constant rate before taking the FFT.
  • #1
mcodesmart
34
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I took the FFT of a signal that was taken at non constant time period (T), but at a sampling frequency(Fs) of 6.5 hz. Can I take the FFT of a signal with non constant T, and does it mean anything? Please see attachment.

Ps. I used Matlabs, FFT command, which i think uses the Cooley–Tukey FFT algorithm
 

Attachments

  • signal y(t).jpg
    signal y(t).jpg
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  • Y(t) fft of signal.jpg
    Y(t) fft of signal.jpg
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  • #2
If the sampling frequency is 6.5Hz, wouldn't that imply a constant time period between samples (153.8msec)? Or what do you mean by T?
 
  • #3
What I mean is that over all, there are 719 data points taken at a non constant T for a total time period of 111.8 sec. From that, I came up with 6.5, but I see that is misleading.

Here are the timing points..

0.1025, 0.2554, 0.4199, 0.5935, 0.7738, 0.9509 ... 111.80

But signal is clearly periodic so I decided to take the FFT to see the frequencies.. But can I do that..
 
  • #4
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1. What is FFT of a signal?

FFT (Fast Fourier Transform) of a signal is a mathematical algorithm that is used to convert a signal from its original domain (typically time or space) to a representation in the frequency domain. This allows for the analysis of the different frequencies that make up the signal and can help identify patterns and characteristics of the signal.

2. How is FFT different from regular Fourier Transform?

FFT is a faster implementation of the traditional Fourier Transform. While the traditional Fourier Transform has a time complexity of O(n^2), FFT has a time complexity of O(nlogn). This makes it more efficient and practical for real-time signal processing.

3. What types of signals can be analyzed using FFT?

FFT can be used to analyze any type of signal that can be represented in the time domain. This includes audio signals, images, and even financial data. However, it is most commonly used in the analysis of signals in fields such as engineering, physics, and telecommunications.

4. How is the FFT of a signal calculated?

The FFT algorithm involves breaking down a signal into smaller segments, applying the Discrete Fourier Transform (DFT) to each segment, and then combining the results to get the final representation in the frequency domain. This process is repeated recursively until the entire signal has been transformed. The specific implementation and steps may vary depending on the programming language or software being used.

5. What are the applications of FFT in science?

FFT has a wide range of applications in various scientific fields. It is commonly used in signal processing for tasks such as noise reduction, filtering, and spectrum analysis. It also has applications in image processing, data compression, and cryptography. In addition, FFT is widely used in scientific research to analyze and interpret data in fields such as acoustics, astronomy, and biomedical engineering.

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